1. Field of the Invention
This invention relates generally to a pulse width modulated signal amplifier, and more particularly is directed to a protecting circuit of a pulse width modulated signal amplifier having a rectifying circuit for rectifying an AC voltage to obtain a DC operating voltage for the amplifier.
Description of the Prior Art
In a prior art pulse width modulated signal amplifier, there is provided at its output side, a low pass filter including an inductance for demodulating an amplified pulse width modulated signal to an audio signal or the like. Normally, forward and backward (positive and negative) currents alternately flow through this low pass filter. However, when the frequency of the output signal is very low, for example, on the order of 20Hz, or when a load impedance is lowered due to short-circuiting of the load, a large current will flow, particularly in one direction, in the low pass filter. This current causes overcharging of a smoothing condenser of a rectifying circuit forming a DC power supply for the amplifier, and hence the level of the DC output voltage of the rectifying circuit rises unacceptably to destroy the smoothing condenser or to damage an amplifying switching element of the amplifier.